A chosid follows every detail of halocho diligently, and even goes above and beyond the letter of the law, while remaining humble and keeping a simple outlook on G-d.

Even though this is a Chabad forum, it is interesting to note the words of the Breslover Rebbe, who said that it is bad to be a chosid in a small town (ie, a place without many chassidim) as it leads to arrogance.

In addition to the religious texts every Jew should be familiar with, such as the Tanach and the Talmud, here are some reading suggestions:

The Shulchon Oruch Horov teaches us how we should conduct ourselves every day as chasidim.

Likutei Omorim (Tanya) teaches us the basics of Chabad Chasidus. It was written not for the tzaddik, nor for the rosho, but for a benoni, a simple person who is neither a tzaddik nor a rosho.

Likutei Sichos, a collection of talks given each week by the Lubavitcher Rebbe, gives us enlightening ideas concerning the parshas hashovua.

The Zohar, the main kabbalistic work. (It is important to have a teacher guide you through the study of kabolo. It can be dangerous if one learns kabolo without understanding what he is reading.) The life of a chosid, such as the minhagim we do as chasidim, is often dictated by kabbalistic principles and teachings.

Sefer Haminhagim lays out the minhagim of Lubavitch.

Simply learning and reading doesn't make a chosid, though. One must dress in a special way to differentiate themselves from the rest of the world, and to please Hashem.

Chasidim wear two head coverings while praying, both a yarmulke and another hat.

Chasidim do not shave their beards. At all.

White button-down shirts and black pants distinguish us from others. For married men, a long black frock coat is also worn.

A gartel is worn by married men under the shirt. It is a belt that separates the heart and the lower body regions during prayer. (This also means that a chosid should strive to always have pure thoughts!)

The tefillin of Rabbeinu Tam are donned after Shacharis, in addition to the usual Rashi tefillin which are worn during Shacharis.

Chasidim should also strive to love and help every Jew, no matter his current religious status. The Lubavitcher Rebbe sent his chasidim to each corner of the world to establish a Jewish presence there and bring Jews back to their heritage.

In general, a chosid should constantly be aware that Hashem is above him and he should conduct himself thus.

This is far from a complete guide but perhaps it should serve as a start.
Remember that not everyone is supposed to be a chosid. But if one feels extreme fervor and fear for Hashem, then there is nothing keeping him from donning the black hat!